Feroxosides A-B, two norlanostane tetraglycosides from the Caribbean sponge Ectyoplasia ferox

Feroxosides A and B, have been isolated from the polar extract of the Caribbean sponge Ectyoplasia ferox. Their structures have been determined to be unusual C-4 nor-lanostane triterpenes glycosylated with a rhamnose containing tetrasaccharide chain, by interpretation of spectral data and chemical degradation. Absolute stereochemistry at C-23 has been determined by application of the modified Mosher method for secondary alcohols. Feroxosides A-B are moderately cytotoxic (IC50 19 μg/mL) against murine monocyte-macrophage cell line.